Feed screw mechanism



March 28, 1944. B R. GRANBERG ETAL 2,345,194

' FEED 'scREw- MECHANISM Filed Jan. 9. 1942 fff am@ mwswvwwwwwwwuw EVMUMNMM, Tamm@ eumwmmmhwmm MTW Patented Mar. 28, 1944 FEED SCREW MECHANISM Bengt R. Granberg and Alfred G. Ericson,vRock ford, Ill., assignors to Sundstrand Machine Tool Co., Rockford, Ill., a corporation of Illinois Application January 9, 1942, Serial No. 426,160

s claims.

'I'his invention relates generally to improvements in feeding mechanism for machine tool slides or work supports, and more particularly to an improved screw and nut device adjustable for eliminating lost motion or backlash between the parts.

It is the general object of the invention to provide a new and improved feed mechanism of the screw and nut type which is simple in construction and readily adjustable to effectually prevent lost motion between the parts during operation. Another object of the invention is to provide animproved feed mechanism of the screw and nut .type arranged to prevent lost motion or backlash during operation of the feed-device in either direction.

A further object of the invention is to provide a feed mechanism of the screw and nut type in which the nut element includes two separate parts, both engaged with the screw element but spaced apart thereon and relativelyadjustable along the axis of the screw for taking up backlash or lost motion, and in which the screw is fixed against rotation and the nuts` are rotatably mounted between thrust bearings, one of which is fixed while the other is axially movable and provided with adjusting means for so moving it to eliminate backlash between the nuts and the screw. f

Other objects and advantages will become apparent from the following description taken -in connection with the accompanying drawing, in which:

Fig. 1 is a vertical section taken through the base or table of a milling machine at the axis of the lead screw and nuts of the feed mechanism.

Fig. 2 is a transverse detail section taken substantially as indicated at line 2-2 on Fig. 1, to show the adjusting means for taking up backlash.

Fig. 3 is a. detail section taken substantially as indicated at line 3-3 on Fig. 1.

While there is shown in the drawing, and described herein, a preferred form of this invention as embodied in a screw and nut feed mechanism for actuating the work table of a milling machine, it is to be understood that the invention is not limited to the specic form or application thus disclosed, and that We intend to cover all modifications and alternative constructions falling within the scope of the invention, as expressed in the appended claims.

As illustrated in the drawing, the work table or slide I is mounted for reciprocation on the base or supporting frame of the machine, of

which portions are seen at Il, and thetable includes end brackets I2, I2 in which there is secured and anchored against rotation a lead screw I3. A pair of nuts I4 and I5 are journaled for rotation in the base II in threaded engagement with the lead screw I3 and each of said nuts is provided with gear teeth, indicated at I6, which mesh with the teeth of a pinion I'l, the latter being an idler connecting the nuts with a driving gear I8. The shaft of the gear I3 is coupled directly to the drive shaft I9 of a motor 20. As shown, the teeth of the idler pinion Il are interrupted at the middle portion of the pinion to provide adequate space for the bail bearings 2l, 2l in. which the inner ends of the nuts I4 and I5 are respectively journaled. Additional bearings 22, 22 are provided for the nuts adjacent their outer ends.

The nut I4 is furnished with a 'ball thrust bea-ring 23 which reacts between said nut and the transaxial shoulder 2lia of a stop collar 24 secured in the base II of the machine. lA ball thrust lbearing 25 for the nut l5 reacts against an adjusting sleeve 2B which is disposed in coaxial relation to the lead screw I3 and surrounding it, said sleeve being suitably guided in the bore IIa of the base in which the journal bearings and thrust4 bearings just mentioned are accommodated. Adjacent its outer end the sleeve 26 is threaded at 21 and engages the internal threads of a collar 2,8 anchored in the base I I. As shown, the collar 28 is screwed into the end of the bore IIa with its ange 28a abutting the terminal shoulder of said bore and with an anchor screw 29 securing it in this position.

As a matter of convenience of construction, the nut I5 includes an enlarged portion intermediate its ends which provides a shoulder I5*al against which the inner race 22a of the ball bearing 22 is lodged. A spacer ring 30 engages the opposite face of the race 22a and provides a seat for one raceway 25a of the thrust bearing 25. The opposite raceway 25h-lodges against the inner end of the sleeve 26 so that axial adjustment of the sleeve 26 thus transmits pressure and movement through the thrust bearing 25 to the shoulder I5it and thus to the nut I5. By virtue of its threaded connection with the base II at 21, a slight rotation of the sleeve 26 will thus act to shift the nut I5 axially in a direction to take up any play or backlash between the threads oi the nuts I4 and I5 and the threads of the lead screw I3. Such rotative adjustment of the sleeve 26 is effected by means of a manually operable worm or screw 3| meshing with suitably formed teeth 32 on the sleeve 26 and carried on the shaft 33 having a squared end 34 which is exposed at one side of the machine for actuation by any suitable form of removable crank or wrench.

While the adjustment of the nut I5 toward the nut I4 by means of the worm 3| and sleeve 26 will exert a compressive force along the axis of the feed screw I3 when the play or backlash has been taken up by such adjustment, it has been found that if the threads are chromium plated the coeflcient of friction is so greatly reduced that this axial pressure may be permanently maintained without imposing an undue load von the drive mechanism and without any rapid deterioration of the threaded 'members through wear. Preferably, the chromium plating is applied to the threads of the lead screw I3 and the nuts I4 and I5 are made from a suitable quality of bearing bronze or other alloy. It is' also ran advantage of the present yconstruction that the adjustment to take up backlash can lbe made while the machine is running and independently of the direction of operation. Thus the effect of the adjustment can -be observed and it can be carried just far enough to take up the play without imposing an unduly severe frictional load on the threads of the feed mechanism.

As shown, the gear teeth I6 of the nuts I4 and I5 are 'formed in separate annular members 35 which are fitted tightly onto the nut members proper and anchored to them by means of keys 3B, as s'een in Fig. 1. This permits independent vreplacement of the threaded portions of the nuts or of the gear members 35 whenever the wear of either of said parts renders this desirable. The keys 36 are supplemented by pins 3'I and securing screws 38 extending through the enlarged portions or fianges I5b 'of the nuts and yinto the ends of the gear members `33, as seen in Fig. 1. The flanges I5b are formed with pockets 39 from which lubricant is delivered to the threads of the screw I3 by way of ducts 40. The Iportions of Fig. l showing these features are taken as indicated at line I-I on Fig. 3, instead of at a strictly vertical plane like the remainder of the section.

W e claim as our invention:

1. In a machine tool which includes a base, a slide mounted for reciprocatio'n on said base, a lead screw secured to said slide against rotation, a pair of nuts spaced apart on the 'screw 'and provided with gear teeth thereon, and ldrive gear- -ingincluding a common pinion engaged "with both nuts to rotate them simultaneously 'iii the same direction, the combination of'a i'xed'thrus't bearing between the outer end of one nutndthe base, an axially movable thrust bearing positioned against the outer end of the other nut,

a sleeve disposed around the screw and interposed between said movable bearing and the base, said sleeve having threaded engagement with the base and being provided with gear teeth, and a worm rotatably supported on the base and -meshing with said teeth operable to rotate the sleeve for adjusting itaxially and thereby shifting the movable nut axially along the screw toward the first nut to take up backlash between the screw and the nuts and place a portion of the screw between the nuts under compression.

2.. In a machine tool which includes a base, a slide mounted for reciprocation on said base, a

. lead screw Vsecured to said slide against rotation,

a. pair of nuts spaced apart on the screw and provided with l"gear teeth thereon, and drive gearing including a common pinion vengaged with both 'n'uts to rotate them simultaneously in the samel direction, vthe 'combination of a fixed thrust bearing between the outer end of one of said nuts and the base, an axially movable thrust bearing positioned against the outer end of the other nut, means interposed between said movable thrust bearing and said base adjustable indepen'de'ntly of the direction of rotation of the nuts to move said lbearing axially and thereby shift one nut toward the other along the screw to take 'up backlash and place a portion of the screw between the nuts under compression.

3. In a machine tool which includes a base, a slide lmo'unted for reciprocation on said base, a lead screw secured 'to said slide against rotation, and 'a Mpair of nuts disposed adjacent each other on the 'screw but spaced apart axially thereon, the combination of means to rotate said nuts simultaneously Yin the same direction comprising 'gear teeth on `each of the nuts intermediate its ends and a `common pinion engaging the gear teeth of both nuts and means to rotate said pinion, a :journal bearing for each nut at its inner e'nd adjacent the other nut and inwardly of the gear teeth, la second 4journalbearing for each nut 4adja'ceifit'its outer lend, .a pair of thrust bearings each reacting between the base and one of the outer :journal bear-ings to .prevent movement of said outenljournal bearings awayfrom .each other, and means-for adjusting one of-said thrust bearings axially at will toward the other to shift one ofthe nuts'towardthe other and to Atake up backlash be'twee'n the nuts and the screw and place the portion of Athe screw between the nuts under compression.

vBENCTT R. GRANBERG.

ALFRED G. AERICSON. 

